Who knew? Aftershocks from the massive New Madrid earthquake over two centuries ago are still happening.
Long-Lived Aftershocks in the New Madrid seismic Zone and the Rest of Stable North America https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023JB026482
The earthquakes in stable North America (the central and eastern US and part of eastern Canada) remain enigmatic and debated. Some scientists think that present-day earthquakes there are long-lived aftershocks of large historic earthquakes; others believe that they are background seismicity concentrated in weak zones and therefore are indicative of future hazard.
Here, we identified long-lived aftershocks by using the nearest-neighbor method, which identifies aftershocks as events statistically correlated with their mainshocks. We found that up to 65% percent of the seismicity between 1980 and 2016 in the New Marid seismic zone is likely aftershocks of the four large earthquakes that occurred there in 1811–1812. Similarly, aftershock activity of the 1886 Charleston earthquake in South Carolina is significant and continuing, while aftershock activity of the 1663 Charlevoix, Québec earthquake has ended.
These results suggest that, in stable continents, aftershock sequences can last decades to centuries, and present-day seismicity in these regions may include both background earthquakes and long-lived aftershocks. Separating them can be useful for earthquake hazard assessment.
I didn’t open the article but will comment anyway. But I wonder if perhaps aftershocks should be comforting rather than fearsome? Maybe continuing aftershocks are showing a constant release of pressure. And when they cease, we should begin to worry because pressure is building up without release, and eventually ends up with a “big” event instead.
That’s exactly how I heard it explained many years ago after one of the big California quakes. Part of the discussion compared CA to other places that have known faults but never seem to have a “big one.” Had to do with the alignment of plates etc etc technical stuff but one of the upshots was if you have a lot of small releases of tension you generally lower the chances of have a catastrophic one.
OK, so what I know about earthquakes you could probably fit in a thimble and have room left over for your finger, but …
It takes just a few minutes for an earthquake on one side of the planet to be detected on the other side. The P waves travel at about the speed of a jet liner - but through, not around the globe according to the research squirrels at Goofy’s Finer Fact Finders, LTD. Therefore if my math is correct, to still be “ringing” 200 years later, the P waves would have had to bounce back and forth through the planet an astonishing 10,512,000 times and still be loud enough to be detected, generously allowing a 10 minute one-way trip. This seems unlikely.
Generally speaking I will defer to people in the field who purport to know what they are doing, but in this case I will reserve judgment until I see further explanation of “how.”
I may be misunderstanding something here. Well, that certainly would be the safe bet.
If P waves travel at about the speed of a jet liner (the fastest jet, the X-15, is about 4,500 mph. And if the diameter of Earth is approximately (it’s not perfectly round) 7,900 miles, wouldn’t it take approximately 1 hour 45 minutes for P waves to travel through the planet? And jet liners are slower than the X-15.